This invention relates to the use of spectral absorbance data, as obtained for example by FTIR spectroscopy, to identify and/or measure the concentration of solutes in a volume of liquid. A common purpose is to identify and measure pollutants in waste water discharge.
In common assignee U.S. Pat. No. 5,218,856, concentration of any given solute in a body of liquid is accurately determined by using an FTIR gas cell to measure the solute depletion as a function of time, making use of the exponential decay of the solute which occurs as a fixed volume of liquid is sparged at a constant air flow rate. This provides an accurate measurement of solute concentration in the body of liquid. The term "sparging" refers to a process of causing an air bubble stream to flow through a volume of water. Solutes in the water combine with the air bubbles, and travel to a gas cell, in which they are subjected to spectral absorption analysis. An IR gas cell in an FTIR spectrometer is preferred as the analytical instrument.
The ease or difficulty of analysis by IR-sparging depends in part on the number of solutes in the water, and on the prior knowledge of their identities. The use of FTIR for multicomponent analysis is limited by the fact that it monitors all components simultaneously. This fact is both a strength and a weakness. On the one hand, it makes it possible to perform a much faster analysis than with a separation technique, such as gas chromatography (GC). But, on the other hand, it makes it difficult, if not impossible, to monitor large numbers of components in a given volume of liquid. Because of the fact that the measured spectrum will be the combination of the spectra of all components present, it is necessary to know in advance the identities of the components that may occur, and to set up a calibration for these components. In contrast, GC separates the various components based on the passage of time. While GC doesn't always positively identify an unknown component, it can determine how many components are present, and can get a good idea of their nature. FTIR is often combined with GC to positively identify the components (GC fractions) once they have been separated. In summary, GCIR can provide the desired data, but it causes a significant loss of time, which the present application seeks to change.
The present invention involves a discovery which permits the individual identification of multiple solutes in a sparging-IR system, without necessitating component separation by the use of chromatography.